This invention relates to corrosion-resistant mixing impellers and more particularly relates to glass coated metal mixing impellers.
Glass coating of metal substrates is well known as, for example, described in U.S. Pat. Nos. RE 35,625; 3,775,164 and 3,788,874. Glass coated mixing impellers are also known as, for example, described in U.S. Pat. Nos. 3,494,708; 4,213,713; 4,221,488; 4,264,215; 4,314,396; 4,601,583 and D 262,791. U.S. Pat. No. 4,601,583 describes glass-coated impellers fitted to a shaft by means of cryogenic cooling to obtain a very tight friction fit. The impellers are dual hub impellers, i.e. two hubs, each carrying two blades. The hubs are placed proximate each other on the shaft so that the blades are oriented 90 degrees to each other about the shaft. The patent also shows multiple impellers spaced from each other upon the shaft, known as a "dual flight" configuration.
Despite it being known that certain glass-coated impellers could be placed upon a shaft, there has been no good glass coated high axial flow impeller available. Such a high axial flow impeller would be desirable to be able to quickly obtain vertical flow to assure quick mixing of an entire tank without concern about separate layering that can occur when only radial flow, e.g. turbine type, impellers are used. U.S. Pat. No. 4,601,583 discloses an impeller having axial flow properties but the axial flow output as measured by its axial flow number is not nearly as good as desired.
High axial flow impellers have been known in metal non-glass coated configurations, e.g. in the form of propellers as commonly found on boats. It was believed that glass coated configurations of those same high flow impellers could not be manufactured because such high axial flow metal impellers have many angles and edges that are generally believed to prevent effective glass coating.